This invention pertains to blowers and more particularly to plastic blowers which are used for handling hot corrosive gases and liquids.
Furnaces, such as those used in heating residences, are sometimes equipped with exhaust blowers which draw the hot products of combustion through one or more heat exchangers and then exhaust the products of combustion to a flu or a vent. In the use of such blowers, a substantial amount of heat is scrubbed from the products of combustion so that the temperature of the products of combustion, after passing through the heat exchangers, is approximately 100.degree. F. The products of combustion contain carbon monoxide, carbon dioxide, as well as corrosive substances such as, for instance, sulfur. Furthermore, the products of combustion contain a large amount of water vapor which may condense in the exhaust blower and, by combining with the corrosive substances, may create a highly corrosive environment for the blower. It is therefore important that such exhaust blowers be able to withstand the corrosive products of combustion as well as the acidic water which may condense from the products of combustion. For that reason, such blowers are preferably constructed of molded thermoplastic material which has a high resistance to corrosion. The blower wheel or impeller of such blowers is thus preferably constructed as a one piece molded plastic part.
A problem in the construction of such blowers is to effectively secure the shaft of a driving electric motor to the plastic impeller. In the prior art, such impellers have been secured to motor shafts by special fastening means such as set screws, keys and key ways, deformable pressure ribs and special pressure flanges which fit over the impeller hub to tighten the hub down on the driving shaft Such arrangements have not been satisfactory due to their complexity and cost, the possibility that the driving shaft may work loose from the impeller during the life of the blower because of vibrations and the like, as well as due to plastic creep or deformation which occurs due to aging of the plastic.
A particular problem which must be overcome in plastic materials which are used for connecting plastic parts to steel parts, is the fact that thermoplastic materials are subject to creep which may cause the driving shaft of the blower to become loosened from the plastic impeller during the life of the blower. Thus it is desirable that a connection be provided which is not subject to this problem. It is also desirable that the attachment arrangement of plastic impellers allow removal of the impeller from the driving motor if servicing of the blower should be necessary. Still further, it is desirable that as few parts as possible be used in the attachment arrangement of the blower impeller to the motor shaft and that the impeller be secured to the motor shaft with a minimum of labor and cost.